Par Genevieve Soucail - 25/10/2005
The detection of distant supernovae being the main scientific dirver of the Deep survey, observations are scheduled with specific time constraints : one observation every 2 or 3 nights for 5 months/year over 5 years. 4 fields are selected which cover the RA distribution over the year. At the end of the survey, the total expected integration time will as high as 33h in u* and g’, 66h in r’ and z’ and 132h in i’. Limiting magnitudes should nearly reach 28, an unprecedented level ever attained on ground-based observations and over a 1 degree scale.
In more details, the observing strategy is fixed by constraints in the detection of supernovae : each "block" of observation has been fixed as follows :
The average rate of "blocks" acquisition, estimated from general statistics of observations in queue mode at CFHT and including weather statistics, is 5.25 "blocks" per dark run. Note that a dark run is considered as long as 18 days of dark and grey time.
- 1h integration time in i’ is the first priority. One exposure is taken every 2-3 nights
- 30mn in r’, 15mn in g’ and 30mn in z’ are obtained the same night or the following one.
- u* observations do not follow these time constraints, but are supposed to be acquired at the same "speed", equivalent to 15mn per "block".
For each filter, the expected limiting magnitudes in the AB system (S/N=5 in a 1.16" diam. aperture) and total integration times are estimated throuhg the last evaluations of MegaPrime performances by using the MegaPrime exposure time calculator DIET :
||Expected integration time after 1 year
||Limiting magnitude (AB)
||Total integration time at the end of the survey
||Limititing magnitude (AB)
|Alpha (2000) ||Dec (2000) ||Comments
||02h 26m 00s
||-04d 30m 00s
|| Embedded in the CFHTLS-W1 field.
- Centered in the Deep area of the VLT-VIRMOS Deep Survey field, in which spectroscopic optical follow-up is taking place at the VLT with VIMOS, up to I_AB=24 at more than 80% completeness.
- Located within the area covered by the XMM-LSS survey : 20 ksec XMM pointings per field.
- Also a GALEX and SIRTF target
||10h 00m 29s
||02d 12m 21s
||Field selected within the area of the Cosmos/ACS project. HST data will be publicly available very rapidly.
- Several multi-wavelength follow-ups on-going or planned (XMM, GALEX, SIRTF, ESO/VIMOS ...). Quick release of the data.
- low extinction field
||14h 19m 28s
||+52d 40m 41s
||Embedded in the CFHTLS-W3 field.
- Located within the ’’Groth Strip’’ area, with low extinction.
- Redshifts available from the Deep II collaboration (I_AB<23.5), obtained with the Keck telescope.
- Also a GALEX target
||22h 15m 31s
||-17d 44m 00s
||Field selected for its lowest extinction field around RA=22h.
- Centered around the quasar LBQS2212-17 in the anti-Leonids area. A deep XMM-Newton exposure (250ksec) publicly available. Source positions and catalogues developped by the XMM SSC are expected to be released soon.
[Dans la même rubrique]